Durability studies of aluminium/ aluminium joints bonded by chlorobutyl rubber-carboxylated nitrile rubber and epichlorohydrin rubber-carboxylated nitrile rubber blends

Two novel rubber blends based on chlorobutyl rubber ( )-carboxylate nitrile rubber ( ) and epichlorohydrin rubber (ECO)-carboxylated nitrile rubber ( ) can be used as adhesives for aluminium/aluminium bonding. Incorporation of silica filler in the blend and carbon black in the blend improves joint strength. The adhesives show remarkable water and salt water resistance. The adhesives based on show remarkable heat and water resistance. Heat stability of the adhesives based on is not satisfactory but can be improved by the application of silane primer on the aluminium surface. Silane primer also improves the paraffin oil resistance. The increase in joint strength resulting from the application of silane primer is due to the formation of Si-O-Al linkages at the aluminium/primer interface.     

Effect of silica filler on aluminum-aluminum bonding by a self-vulcanizable blend based on chlorobutyl rubber and carboxylated nitrile rubber

Silica filler improves the aluminum-aluminum bonding by a self-vulcanizable rubber blend based on chlorobutyl rubber and carboxylated nitrile rubber. The joint peel strength depends on the filler loading, the state of cure, the molding temperature, and the adhesive film thickness. The higher peel strength in the filled adhesive system is due to filler reinforcement resulting in tear path deviation and the formation of Si—O—Al linkage at the aluminum-adhesive interface. Maximum peel strength was obtained at 10 phr filler loading, when the molding temperature was 180°C and the molding pressure was 0.35 MPa.     

Peel Strength of Aluminium-Aluminium Joints Bonded by Adhesive Based on Carboxylated Nitrile Rubber-Chlorobutyl Rubber Blend

The peel strength of aluminium-aluminium joints bonded by an adhesive based on carboxylated nitrile rubber and chlorobutyl rubber was found to depend on surface topography and use of a silane primer. Anodization causes a marginal increase in bond strength while the silane primer improves the adhesive joint strength remarkably.

The peel strength was also found to be dependent on test conditions (test rate and temperature). The threshold peel strength value obtained by measurements at low peel rate and high test temperature was found to depend on the type of failure during peeling (cohesive or interfacial) which, in turn, is controlled by the presence of silica filler in the adhesive. Two different threshold values of peel strength were obtained: 60 N/m for interfacial failure (in silica-filled adhesive), 140 N/m for cohesive failure (in unfilled adhesive).     

Bound rubber in chlorobutyl compounds: Influence of filler type and storage time

Bound rubber (BdR) is considered as a measure of the filler–polymer interaction in rubber compounds. The variation of the BdR content with storage time was studied in chlorobutyl compounds filled with fillers like carbon black, carbon–silica dual phase filler (CSDPf), silica, and nanoclays. The effect of the addition of a silane coupling agent on the BdR in carbon black and silica filled compounds was also studied. The BdR content increased with storage time in all compounds. The increase in BdR was higher during the initial 15 days of storage. Thereafter there was only a marginal increase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 715–720, 2006     

Vulcanization of carboxylated nitrile rubber (XNBR) by zinc peroxide

The vulcanization of carboxylated nitrile rubber (XNBR) with zinc peroxide, which produces ionic crosslinks, has been studied in relation to vulcanization time. Vulcanized compounds present two transitions, corresponding to the glass transition of the polymer at low temperatures and the ionic transition resulting from the formation of ionic aggregates. Both transitions are displaced to higher temperatures with increasing crosslink density. The ionic associations which give rise to high values of mechanical properties disappear on exposure of the vulcanized compounds to saturated ammonia vapour. This treatment produces a decreased crosslink density resulting in the disappearance of the ionic transition. When the action of ammonia is terminated by immersion in solvent followed by drying, the original crosslink density is recovered and the ionic transition reappears, although at higher temperatures. However, with increasing crosslink density, the difference between the temperatures at which both transitions take place diminishes. All these factors can be interpreted as reflecting the generation of a new and more compatible arrangement of the newly-appearing ionic clusters. © 1999 Society of Chemical Industry     

Modification of ethyl 2-cyanoacrylate using silica and nitrile butadiene rubber to achieve high thixotropy and low internal stress

A mixture of fumed silica and nitrile butadiene rubber (NBR) is used to improve the viscosity and thixotropy of ethyl 2-cyanoacrylate (ECA) and to reduce the internal stress of ECA. Rheological characteristics of ECA/silica, ECA/NBR, and ECA/silica/NBR are measured using a rheometer and are presented using the viscosity and thixotropic index. The pristine and modified ECA were characterized using Fourier transform infrared spectrometer (FT-IR) and Thermal gravity analysis (TGA). The impact of additives on curing internal stress of ECA is measured and analyzed. Results shown that addition of fumed silica and NBR effectively improve the viscosity of ECA blends, which increases with an increased content of both additives. Thixotropic ECA/silica/NBR shows an apparent shear-thinning character and is well fitted by a power law equation. FT-IR spectra and TGA analysis indicated that the thixotropy of the obtained ECA/silica/NBR blends is mainly attributed to silica via the creation of hydrogen bonds between silica particles and between silica and polymers, and a synergistic effect between silica and NBR is shown to improve viscosity. The modified ECA showed considerable stability and their viscosity were slightly increased after 30 days. The presence of NBR is beneficial for silica dispersion in the ECA matrix and for a smooth surface of cured ECA. The added silica and NBR can alleviate the internal stress of the cured adhesive layer, and NBR plays a significant role in reducing internal stress. This work is devoted to developing thixotropic and low-shrinkage cyanoacrylate-based adhesives.     

Vulcanization of carboxylated nitrile rubber (XNBR) by a mixed zinc peroxide–sulphur system

Vulcanization of carboxylated nitrile rubber (XNBR) with a mixed system based on zinc peroxide and sulphur accelerators produces materials with favourable mechanical properties because of the formation of ionic aggregates which give the vulcanized compounds a certain rigidity. These properties are drastically reduced by the effect of saturated ammonia vapour which plasticizes the ionic aggregates. This plasticization, however, is reversible and the aggregates can be regenerated by addition of a solvent, which results in recovery and even improvement of the original properties such as stress at constant deformation, tensile strength, crosslinking density and storage modulus. The temperatures of the two transitions observed in the relaxation spectra, the glass transition of the polymer and the ionic transition corresponding to ionic aggregates, are displaced to higher values when ionic structures are regenerated. © 2000 Society of Chemical Industry     

A study on the curing kinetics of epoxycyclohexyl polyhedral oligomeric silsesquioxanes and hydrogenated carboxylated nitrile rubber by dynamic differential scanning calorimetry

A new organic–inorganic hybrid material was prepared through reactive blending of hydrogenated carboxylated nitrile rubber (HXNBR) with epoxycyclohexyl polyhedral oligomeric silsesquioxanes (epoxycyclohexyl POSS). The structure of the composite was characterized by Fourier transform infrared spectroscopy (FTIR) and solid‐state ¹³C Nuclear Magnetic Resonance spectra (solid‐state ¹³C‐NMR). The differential scanning calorimetry (DSC) at different heating rates was conducted to investigate the curing kinetics. A single overall curing process by an nth‐order function (1 ? α)ⁿ was considered, and multiple‐heating‐rate models (Kissinger, Flynn–Wall–Ozawa, and Crane methods) and the single‐heating‐rate model were employed. The apparent activation energy (E_a) obtained showed dependence on the POSS content and the heating rate (β). The overall reaction order n was practically constant and close to 1. The isoconversion Flynn–Wall–Ozawa method was also performed and fit well in the study. With the single‐heating‐rate model, the average E_a for the compound with a certain POSS content, 66.90–104.13 kJ/mol was greater than that obtained with Kissinger and Flynn–Wall–Ozawa methods. Furthermore, the calculated reaction rate (dα/dt) versus temperature curves fit with the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Tensile stress relaxation of short‐coir‐fiber‐reinforced natural rubber composites

The stress relaxation behavior of natural rubber (NR) and its composites reinforced with short coir fibers under tension was analyzed. The rate of stress relaxation was a measure of the increase in the entropy of the compounds: the higher the rate was, the greater the entropy was. At lower strain levels, the relaxation mechanism of NR was independent of strain level. However, the rate of relaxation increased with the strain level. Also, the strain level influenced the rate of stress relaxation considerably in the coir‐reinforced NR composites. However, the relaxation mechanisms of both the unfilled compound and the composite were influenced by the strain rate. The rate of relaxation was influenced by fiber loading and fiber orientation. From the rate of stress relaxation, we found that fiber–rubber adhesion was best in the composite containing fibers subjected to a chemical treatment with alkali, toluene diisocyanate, and NR solutions along with a hexaresorcinol system as a bonding agent. In this study, the stress relaxation curves could not be viewed as segments with varying slopes; however, a multitude of inflection points were observed on the curves. Hence, we propose neither a two‐step nor three‐step mechanism for the coir‐fiber‐reinforced NR composites as reported for some other systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 96–104, 2004     

硫化发泡体系对硅橡胶泡沫材料应力松弛性能的影响

考察了过氧化二异丙苯/N,N-二亚硝基五次甲基四胺(DCP/H)、2,5-二甲基-2,5-二叔丁基过氧化己烷/偶氮二甲酰胺(双二五/AC)和过氧化苯甲酰(BPO)/AK 3种硫化发泡体系及助交联剂TAIC对硅橡胶泡沫材料力学性能和压缩应力松弛性能以及泡孔结构的影响。结果表明,DCP/H硫化发泡体系的力学性能和应力松弛性能优于双二五/AC和BPO/AK,添加适量助交联剂TAIC有助于进一步降低硅橡胶泡沫材料的应力松弛性能。扫描电镜(SEM)观察发现,DCP/H硫化发泡体系对应的硅橡胶发泡材料泡孔较小且分布均匀,当加入适量的助交联剂TAIC后,硅橡胶泡沫材料的泡孔更加细小均匀。     

Structure and properties of nitrile rubber (NBR)–clay nanocomposites by co‐coagulating NBR latex and clay aqueous suspension

Nitrile rubber (NBR)–clay nanocomposites were prepared by co‐coagulating the NBR latex and clay aqueous suspension. Transmission electron microscopy showed that the silicate layers of clay were dispersed in the NBR matrix at the nano level and had a planar orientation. X‐ray diffraction indicated that there were some nonexfoliated silicate layers in the NBR–clay nanocomposites. Stress–strain curves showed that the silicate layers generated evident reinforcement, modulus, and tensile strength of the NBR–clay nanocomposites, which were significantly improved with an increase in the amount of clay, and strain‐at‐break was higher than that of the gum NBR vulcanizate when the amount of clay was more than 5 phr. The NBR–clay nanocomposites exhibited an excellent gas barrier property; the reduction in gas permeability in the NBR–clay nanocomposites can be described by Nielsen's model. Compared with gum NBR vulcanizate, the oxygen index of the NBR–clay nanocomposites increased slightly. The feasibility of controlling rubber flammability via the nanocomposite approach needs to be evaluated further. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3855–3858, 2003